1. Field of the Invention
The present invention relates to a hard disk drive. More particularly, the present invention relates to a disk pack of a hard disk drive which includes a spindle motor hub and disks mounted to the spindle motor hub.
2. Description of the Related Art
Hard disk drives (HDDs) are memory devices which record and reproduce data by converting digital electric pulses to a magnetic field and vice versa. To this end, a hard disk drive includes at least one disk having a number of tracks along which data is recorded, a spindle motor for rotating each disk, a read/write head which can write magnetic data onto the disk and read magnetic data from the disk, and an actuator arm for positioning the head above a particular track of the disk and maintaining the read/write head a predetermined height above the disk while the head is reading or writing data from or onto the disk. With such components, HDDs can access a large amount of data quickly. Therefore, HDDs have been widely used as auxiliary memory devices of computer systems.
Recent advances in the fabrication of hard disks have increased the number of TPI (tracks per inch) and BPI (bits per inch; a measure of the amount of data that can be recorded along a track). That is, recent advances have increased the capacity of HDDs so that HDDs can be made more compact and therefore, can be employed in a wider range of devices. In particular, there is a large demand for compact HDDs which can be used in portable electronic devices such as notebooks, personal digital assistants (PDAs), and mobile phones. In fact, a compact HDD whose disk has a diameter of 0.8 inches, i.e., a diameter similar to that of a coin, has been recently developed for use in mobile phones.
As briefly mentioned above, the disk is rotated by a spindle motor when the HDD is operating. Therefore, vibrations are generated due to the rotation of a disk. These vibrations must be attenuated to ensure that the HDD operates reliably and at full capacity. Problems related to disk vibrations will now be discussed below with reference to a conventional HDD shown in FIG. 1. The conventional HDD has two disks 111 and 112 coupled to a spindle motor. Also, an annular spacer 114 is disposed on the spindle motor hub 120 between the disks 111 and 112. A clamp (not shown) is disposed the spindle motor hub 120 and the second disk 112. The clamp is secured by a screw (also not shown) onto the spindle motor hub 120 so as to press down against the upper surface of the second disk 112 and thereby clamp the disks 111 and 112 to a flange of the spindle motor hub 120. Therefore, the disks 111 and 112 rotate together with the spindle motor hub 120 during the operation of the HDD.
In the conventional HDD, however, a gap G is present between the disks 111 and 112 and a side wall 121a of the spindle motor hub 120 due to the tolerance provided to facilitate the mounting of the disks 11 and 112 onto the spindle motor hub 120. The gap G prevents at least one of the disks 111 and 112 from rotating at a constant speed because, for example, the disk rotates while inclined relative to the axis of rotation. As a result, vibrations are produced at one side of the disk during its rotation.
It is relatively easy to mount the disks 111 and 112 to the spindle motor hub 120 when the gap G is large, i.e., when the inner diameter of each of the disks 111 and 112 is much larger than that of the spindle motor hub 120. In this case, however, the rotation of the disks 111 and 112 becomes severely eccentric relative to the axis of rotation of the spindle motor hub 120. As a result, the disks 111 and 112 vibrate excessively, thereby preventing the HDD from functioning properly. Tightening the screw that secures the clamp to the spindle motor hub 120 can obviate this potential problem. However, if the clamp screw is tightened too much, the inner circumferential (ID) portion of each of the disks 111 and 112 is pressed hard against the side wall 121a of the spindle motor hub 120. In this case, the ID portion of each of the disks 111 and 112 is likely to warp, thereby reducing the capacity and reliability of the HDD.
Thus, the gap G should be as small as possible to ensure that the disks 111 and 112 will rotate smoothly with the spindle motor hub 120. That is, the inner diameter of each of the disks 111 and 112 should be matched as close as possible to the outer diameter of the upper end portion of the spindle motor hub 120. However, such tight tolerances compromise the ability of the disks 111 and 112 to be mounted to the spindle motor hub 120. In particular, the first disk 111 may scratch the side wall 121a of the spindle motor hub 120 as the first disk 111 is lowered onto the upper portion of the spindle motor hub 120. In this case, particles are generated which causes other problems in the HDD.